The only places I can find candy melts are Big W and Spotlight, for $10 a bag. Is there a more affordable option out there?

I don't live in Australia, but I know in the US we have several different kinds of "candy coating" (for dipping strawberries, pretzels, etc.) available in the grocery stores at a reasonable price and it is virtually the same thing as candy melts.  You might check the baking isle and give them a try.